1. Field of the Invention
The present invention relates to a memory, and more specifically, to a memory having a voltage switch circuit with one bias voltage changed in each state of conditioning.
2. Description of the Prior Art
Memory devices are electronic devices arranged to store electrical signals. The non-volatile memory does not lose its data when the system or device is turned off and may be implemented as a MOS transistor that has a source, a drain, an access or a control gate, and a floating gate. It is structurally the same as standard MOSFET except its gate is floating, which is electrically isolated. There are many structural variations of MOS devices to enhance the operation or reduce the size of non-volatile memory devices.
Considerations including purpose of the device, power consumption, size, retention capacity and duration may influence design of non-volatile memory devices. For example, some non-volatile memory devices may be categorized as floating gate or charge-trapping from a programming perspective.
Non-volatile memory devices may be implemented as non-volatile memory arrays that include a plurality of non-volatile memory cells arranged in rows and columns. In general, 1T non-volatile memory cells operate as follows. During an erase operation, electrons are removed from a floating gate of the non-volatile memory cell, thereby lowering the threshold voltage of the non-volatile memory cell. During a program operation, electrons are injected into the floating gate of the non-volatile memory cell, thereby raising the threshold voltage of the non-volatile memory cell. Thus, during program and erase operations, the threshold voltages of selected non-volatile memory cells are changed. During a read operation, read voltages are applied to selected non-volatile memory cells. In response, read currents flow through these selected non-volatile memory cells.
Certain types of nonvolatile memory devices, circuits employing floating-gate devices, high-voltage drivers and other circuits fabricated in logic CMOS require relatively high voltages (e.g., 10 volts in a 3.3 volt CMOS process). In all these circuits, switches are required to selectively apply the high voltages to specific circuit elements.
Tolerating a high-voltage supply, generating intermediate voltages, as well as generating high-voltage drive signals from logic low-voltage signals while minimizing power consumption, are substantial design parameters for switch circuits adapted to program memory devices.